During each Sonar analysis, the notifications are computed for each user who has subscribed to notifications. Users are notified on new violations introduced on their favourite projects during the first differential view period (Period 1).
Then, in asynchronous way, emails on those notifications are sent to users.
To set the delay between processing of notification queue, set the property sonar.notifications.delay (in seconds) in conf/sonar.properties.
Note that sometimes there could be some discrepancy between values displayed in the email and values displayed on the web interface.
This happens if another analysis has been run between the sending of the mail and you clicking on the link to the Violations drill-down in the email.
In order to be able to send emails, you should first configure the email settings. Go to Configuration > General Settings > Email:
Once the email service is configured each user can subscribe to event notifications.
Each logged in user can subscribe to notification by going to Configuration > My Profile and tick the events they wants to subscribe to: